Wide-angle projection zoom lens and projection type display apparatus

ABSTRACT

A wide-angle projection zoom lens includes, in order from the magnification side: a first group that remains stationary during zooming and has a negative refractive power; second to fourth groups that are movable independently from each other during zooming; a fifth group that remains stationary during zooming and has a positive refractive power. The projection zoom lens is configured to be telecentric on the reduction side. The first group includes five lenses having negative, negative, negative, positive, negative refractive powers. During zooming from the wide-angle end to the telephoto end, the first group and the fifth group remain stationary, and the second to fourth groups are movable in a direction of the optical axis so as to narrow a space between the first group and the second group and widen a space between the fourth group and the fifth group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-088032 filed on Mar. 31, 2009; the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a zoom lens used as a projection lens for a projector apparatus and the like. In particular, the invention relates to a wide-angle projection zoom lens suitable for projecting an original image, which is formed by a light valve such as a liquid crystal display element or a DMD (digital micro mirror device), onto a screen in an enlarged manner. And, the present invention relates to a projection type display apparatus equipped with the zoom lens.

2. Related Art

Recently, so-called front projection type projector apparatuses for projecting an image onto a screen in front of the apparatus are widely used for school education, corporate job training, presentation, and the like.

In the projection lenses provided in the front projection type projector apparatuses, there is a demand that the lenses have a compact configuration, a wide angle of view, and a zoom function in consideration of adaptability to an installation condition and mobility of the apparatus.

In order to cope with the demand, there are proposed projection zoom lenses disclosed in the following Patent Document 1 (JP-A-2003-015038), Patent Document 2 (JP-A-2005-292260) and Patent Document 3 (JP-A-2008-309897).

In the lenses disclosed in Patent Documents 1 and 2, a half angle of view thereof at the wide-angle end is less than 45 degrees. However, recently, there has been a demand for a wide-angle projection zoom lens having a half angle of view of 45 degrees or more at the wide-angle end while maintaining favorable optical performance.

In fixed-magnification projection lenses provided in rear projection apparatuses, a lens having a half angle of view of 45 degrees or more has been known. However, in the case of a zoom lens, when the half angle of view of 45 degrees or more is intended to be achieved, it is difficult to maintain a favorable optical performance from the wide-angle end to the telephoto end. In particular, it is also difficult to correct satisfactorily on-axis aberrations such as spherical aberration common to angles of view (image heights) and off-axis aberrations such as distortion and image field curvature varied with the angles of view while balancing these aberrations. Further, there is also a problem in that the size of the lens system of the lens group disposed close to the magnification side increases and thus it is difficult to achieve compactness. For this reason, the demanded zoom lens has not been embodied.

On the other hand, the lens disclosed in Patent Document 3 is a projection type zoom lens having a speed of F1.8, a half angle of view ω of 45 degrees or more at the wide-angle end, and a zoom of 1.3 times. However, in such a zoom lens, if a higher speed is intended to be achieved, it becomes extremely difficult to design the optical system thereof. In particular, a projector set is required to secure a relative illumination of around 80%, and there are many cases where only the projection lens is required to secure a relative illumination of 50%. If the ratio of the relative illumination is intended to be increased, as an angle of view thereof becomes wider, it becomes more difficult to improve resolution performance in the periphery thereof. Thus, this causes an increase in costs.

In addition, in order to improve optical performance, for example, two aspheric lenses may be disposed in the lens system. However, unlike a spherical lens, sometimes an aspheric lens may be required to have eccentricity adjusted after assembly thereof since it is difficult to perform centering on each single element of the lens. Hence, there has been a demand for simplification in optical adjustment.

SUMMARY

An illustrative aspect of the invention is to provide a wide-angle projection zoom lens capable of achieving a wide angle of view, maintaining favorable optical performance, achieving compactness, and simplifying eccentricity adjustment for aspheric lenses while improving speed, and to provide a projection type display apparatus equipped with the zoom lens.

According to an aspect of the invention, a wide-angle projection zoom lens, which is telecentric on the reduction side, according to an aspect of the invention includes, in order from a magnification side: a first lens group having a negative refractive power; a second lens group having a positive refractive power; a third lens group having a negative refractive power; a fourth lens group having a positive refractive power; and a fifth lens group having a positive refractive power.

During zooming from the wide-angle end to the telephoto end, the first lens group and the fifth lens group remain stationary, and the second lens group, the third lens group, and the fourth lens group are movable in a direction of an optical axis so as to narrow a space between the first lens group and the second lens group and widen a space between the fourth lens group and the fifth lens group.

The first lens group includes five lenses having negative, negative, negative, positive, negative refractive powers in order from the magnification side, and in the first lens group, the negative lens closest to the magnification side and the negative lens closest to the reduction side are formed as aspheric lenses made of plastic.

Further, it is preferable that the second lens group includes two positive lenses.

Furthermore, it is preferable that the third lens group includes a negative lens and a positive lens in order from the magnification side, a surface of the negative lens on the reduction side is formed as a concave surface, and a surface of the positive lens on the magnification side is formed as a convex surface.

Further, it is preferable that the fourth lens group includes, in order from the magnification side, a negative meniscus lens convex toward the magnification side, a first cemented lens having a cemented surface formed in a shape concave toward the magnification side, a second cemented lens having a cemented surface formed in a shape concave toward the reduction side, and a positive lens.

Furthermore, it is preferable that the fourth lens group includes, in order from the magnification side, a negative meniscus lens convex toward the magnification side, a three-element cemented lens having a first cemented surface formed in a shape concave toward the magnification side and a second cemented surface formed in a shape concave toward the reduction side in order from the magnification side, and a positive lens.

Further, it is preferable that the fifth lens group includes a single positive lens.

According to another aspect of the invention, a projection type display apparatus includes: a light source; a light valve; an illumination optical unit guiding rays originated from the light source into the light valve; and the wide-angle projection zoom lens, which is telecentric on the reduction side, having any one of the above-mentioned configurations. In the apparatus, the rays originated from the light source are optically modulated by the light valve, and are projected onto a screen by the wide-angle projection zoom lens.

Furthermore, the “negative lens” means a lens having a negative refractive power at least in a paraxial region.

Further, the “magnification side” means a projection target side (a screen side). Also, in the case of reduced projection, the screen side is also referred to as the magnification side for convenience of description. On the other hand, the “reduction side” means an original-image display region side (a light valve side). Also, in the case of reduced projection, the light valve side is also referred to as the reduction side for convenience of description.

As described above, in the wide-angle projection zoom lens according to the aspect of the invention, the five lens groups are arranged to have negative, positive, negative, positive, and positive refractive powers in order from the magnification side. During zooming from the wide-angle end to the telephoto end, the first lens group and the fifth lens group remain stationary, and the respective second to fourth lens groups are independently movable in the direction of the optical axis so as to narrow the space between the first lens group and the second lens group and widen the space between the fourth lens group and the fifth lens group.

The first lens group includes five lenses having negative, negative, negative, positive, negative refractive powers in order from the magnification side, and in the first lens group, the negative lens closest to the magnification side and the negative lens closest to the reduction side are formed as aspheric lenses made of plastic.

With such a configuration, it is possible to obtain a projection type display apparatus and a wide-angle projection zoom lens capable of achieving a wide angle of view, maintaining favorable optical performance, and achieving compactness while improving speed.

In particular, in the first lens group, the negative lens closest to the magnification side is formed as an aspheric lens. Thus, it is possible to make a ray, which exits at a large angle of view, out of all the rays pass the position farthest from the optical axis in the lens system. Hence, this configuration is remarkably effective in correcting distortion and image field curvature.

Further, as described above, in the aspects of the invention, the negative lens closest to the reduction side in the first lens group is formed as an aspheric lens. Instead of this, for example, in the fourth lens group or the fifth lens group, an aspheric lens may be disposed. In this case, it is also possible to exhibit the effect on the optical performance. However, since it is difficult to apply the centering, which can be performed by the spherical lens itself, to the aspheric lens, adjusting eccentricity thereof separately is required. Accordingly, as described in the aspect of the invention, by providing the reduction side aspheric surface so as to be closest to the reduction side in the first lens group, it is possible to adjust the eccentricities of the two aspheric lenses only within the first lens group which remains stationary during zooming, and it is also possible to simplify further an operation for the adjustment of the eccentricities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a detailed configuration diagram illustrating a wide-angle projection zoom lens (the wide-angle end) according to Example 1.

FIG. 2 is a configuration diagram illustrating arrangement of lens groups in the wide-angle end (W) and the telephoto end (T) of the wide-angle projection zoom lens according to Example 1.

FIG. 3 is a detailed configuration diagram illustrating a wide-angle projection zoom lens (the wide-angle end) according to Example 2.

FIG. 4 is a configuration diagram illustrating arrangement of lens groups in the wide-angle end (W) and the telephoto end (T) of the wide-angle projection zoom lens according to Example 2.

FIG. 5 is a detailed configuration diagram illustrating a wide-angle projection zoom lens (the wide-angle end) according to Example 3.

FIG. 6 is a configuration diagram illustrating arrangement of lens groups in the wide-angle end (W) and the telephoto end (T) of the wide-angle projection zoom lens according to Example 3.

FIG. 7 is a detailed configuration diagram illustrating a wide-angle projection zoom lens (the wide-angle end) according to Example 4.

FIG. 8 is a configuration diagram illustrating arrangement of lens groups in the wide-angle end (W) and the telephoto end (T) of the wide-angle projection zoom lens according to Example 4.

FIG. 9 is a diagram illustrating aberrations of the wide-angle projection zoom lens according to Example 1.

FIG. 10 is a diagram illustrating aberrations of the wide-angle projection zoom lens according to Example 2.

FIG. 11 is a diagram illustrating aberrations of the wide-angle projection zoom lens according to Example 3.

FIG. 12 is a diagram illustrating aberrations of the wide-angle projection zoom lens according to Example 4.

FIG. 13 is a schematic configuration diagram illustrating a projection type display apparatus according to an embodiment.

DETAILED DESCRIPTION

Hereinafter, the exemplary embodiments of the invention will be described with reference to the accompanying drawings. FIG. 1 shows a wide-angle projection zoom lens according to an embodiment of the invention, and is a lens configuration diagram of Example 1 to be described later. The lens is described below as a representative embodiment. Furthermore, in the drawing, the reference sign Z represents the optical axis.

The wide-angle projection zoom lens according to the embodiment includes, in order from the magnification side (the screen side): a first lens group G₁ that remains stationary during zooming, has a negative refractive power, and is used for focusing; second to fourth lens groups G₂ to G₄ (the second lens group G2 having a positive refractive power, the third lens group G₃ having a negative refractive power, and the fourth lens group G₄ having a positive refractive power) as three movable zoom lens groups that are movable independently from each other during zooming; a fifth lens group G₅ that remains stationary during zooming, has a positive refractive power, and is used to fix a position of a pupil (to prevent the position of the exit pupil in the whole system from changing during zooming). The projection zoom lens is configured to be telecentric (or substantially telecentric) on the reduction side.

In the wide-angle projection zoom lens according to the embodiment, during zooming from the wide-angle end to the telephoto end, the first lens group G₁ and the fifth lens group G₅ remain stationary, and the second lens group G₂, the third lens group G₃, and the fourth lens group G₄ are movable in a direction of the optical axis Z so as to narrow a space between the first lens group G₁ and the second lens group G₂ and widen a space between the fourth lens group G₄ and the fifth lens group G₅.

Furthermore, in the wide-angle projection lens according to the embodiment shown in FIG. 1, rays emitted from the right side of the drawing and containing image information displayed on an image display surface 1 of a light valve are incident on the wide-angle projection lens through a glass block 2, and are projected in an enlarged manner on a screen on the left side of the drawing. In FIG. 1, only one image display surface 1 is illustrated for convenience of description, but in some projection type display apparatuses, there are arranged three light valves for three primary color rays into which rays emitted from a light source are separated by using a color separation optical system, thereby enabling full-color-image display (refer to FIG. 13). By arranging a color synthesizing means such as a cross dichroic prism (which may be a glass block as described in some examples) on the glass block 2, it is possible to synthesize the three primary color rays.

The first lens group G₁ includes, in order from the magnification side (the screen), five lenses (first lens L₁ to fifth lens L₅) having negative, negative, negative, positive, negative refractive powers, and is configured to adjust a focal length by moving all the lenses in the direction of the optical axis Z or by moving (floating) the fourth lens L₄ and the fifth lens L₅ so as to change the space therebetween. Furthermore, in the first lens group G₁, the first negative lens (the first lens L₁), which is the negative lens closest to the magnification side, and the fifth negative lens (the fifth lens L₅), which is the negative lens closest to the reduction side, are formed as aspheric lenses made of plastic.

As described above, since the first lens group G₁ is configured to include, in order from the magnification side, five lenses (the first lens L₁ to fifth lens L₅) having negative, negative, negative, positive, negative refractive powers, it is possible to suppress an increase in diameter of the first lens group G₁ and achieve compactness as a whole while increasing an angle of view at the wide-angle end.

Further, in the first lens group G₁ used for focusing, the first negative lens (the first lens L₁) and the fifth negative lens (the fifth lens L₅) in order from the most magnification side are formed as aspheric lenses. Thereby, in the first lens group G₁ in which the angle of view and the optical path are significantly changed by zooming, the three lenses (the second lens L₂, third lens L₃ and the fourth lens L₄) are inserted, and thereby an aspheric surface is disposed to separate the lens group into the front and the rear. As a result, it is possible to correct aberrations satisfactorily from the wide-angle end to the telephoto end.

The aspheric surface of the first lens L₁ is suitable for correcting aberrations according to the angles of view so as to cope with off-axis aberrations such as distortion and image field curvature. The aspheric surface of the fifth lens L₅ is suitable for correcting aberrations common to angles of view so as to cope with the on-axis aberrations such as spherical aberration. The reason is that, since the first lens group G₁ is configured to mainly include the negative lenses as described above, the diameter of rays, which are propagated toward respective image points, can be decreased in the first lens L₁ and can be increased in the fifth lens L₅ mostly on the telephoto side.

Further, since the fifth lens L₅ of the first lens group G₁ is formed as a reduction-side aspheric lens, it is possible to adjust the eccentricities of the two aspheric lenses only within the first lens group G₁ which remains stationary, and it is also possible to simplify further an operation for the adjustment of the eccentricities.

Further, since the second lens group G₂ is configured to include two positive lenses, it is possible to secure speed efficiently and reduce various aberrations while employing a small number of lenses.

Further, the third lens group G₃ includes, in order from the magnification side, a negative lens and a positive lens. In addition, the reduction side surface of the negative lens is formed as a concave surface, and the magnification side surface of the positive lens is formed as a convex surface. With such a configuration, similarly to the above, it is possible to secure speed efficiently and reduce various aberrations while employing a small number of lenses.

Further, the fourth lens group G₄ includes, in order from the magnification side, a negative meniscus lens convex toward the magnification side, a first cemented lens having a cemented surface formed in a shape concave toward the magnification side, a second cemented lens having a cemented surface formed in a shape concave toward the reduction side, and a positive lens. Alternatively, the fourth lens group G₄ includes, in order from the magnification side, a negative meniscus lens convex toward the magnification side, a three-element cemented lens having a first cemented surface formed in a shape concave toward the magnification side and a second cemented surface formed in a shape concave toward the reduction side in order from the magnification side, and a positive lens. With such a configuration, it is possible to correct various aberrations, in particular, chromatic aberration. Furthermore, by employing the three-element cemented lens, it is possible to improve the effect of the chromatic aberration correction. On the other hand, by employing two two-element cemented lenses as compared with the case of using the three-element cemented lens, it is possible to reduce further the adverse effect caused by heat expansion.

Further, it is preferable that the fourth lens group G₄ include two cemented surfaces arranged therein. However, there is a concern that a trouble (such as detachment of an adhesive) may be caused in the cemented portions by the effect of heat when the position, at which the diameter of the rays is narrowed down, approaches the vicinities of the cemented surfaces. In the embodiment, for example, in all the examples as shown in FIGS. 2, 4, 6, and 8, the position P, at which the principal rays intersect with each other, is located on the magnification side from the fourth lens group G₄. Therefore, the configuration is made so as to be able to prevent the problem being caused in the cemented portions as described above.

Further, since the fifth lens group G₅ includes a single positive lens, it is possible to simplify the configuration, and thus this is preferable.

Furthermore, in the operation of adjusting a focal length of the first lens group G₁, by moving (floating) the fourth lens L₄ and the fifth lens L₅ so as to change the space between the two lenses as described above, it is possible to reduce the weight of the movable lenses, and thus this is preferable.

Next, an example of the projection type display apparatus equipped with the above-mentioned projection type zoom lens is described with reference to FIG. 13. The projection type display apparatus shown in FIG. 13 has transmissive liquid crystal valves 11 a to 11 c as light valves. In the apparatus, the wide-angle projection zoom lens according the above-mentioned embodiment is used as a wide-angle projection zoom lens 10. Further, although not shown, between the light source 20 and the dichroic mirror 12, white rays, which are originated from a light source 20, are incident through an illumination optical section on the transmissive liquid crystal valves 11 a to 11 c, which correspond to three color rays (G light, B light, and R light) respectively, and are optically modulated, and then colors of the rays are synthesized by a dichroic prism 14, thereby projecting the rays on a screen, which is not shown, through the projection type zoom lens 10. The apparatus includes dichroic mirrors 12 and 13 for color separation, the cross dichroic prism 14 for color synthesis, condenser lenses 16 a to 16 c, and total reflection mirrors 18 a to 18 c. Since the projection type display apparatus according to the embodiment employs the wide-angle projection zoom lens according to the embodiment, it is possible to achieve a speed of F1.70 at the wide-angle end, increase the half angle of view ω up to 45 degrees or more at the wide-angle end, and decrease the size of the apparatus while providing a zoom function. As a result, it is possible to improve convenience and mobility of the apparatus remarkably.

Furthermore, the wide-angle projection zoom lens according to the embodiment of the invention is not limited to be used as a wide-angle projection zoom lens of a projection type display apparatus using a liquid crystal display panel. However, the projection zoom lens may be used as a wide-angle projection zoom lens of an apparatus using another optical modulation means such as a DMD.

Hereinafter, specific examples of the wide-angle projection zoom lens according to the embodiment of the invention will be described. In FIGS. 3 to 8 showing the configurations of Examples 2 to 4, the members having the same effect as Example 1 will be referenced by the same reference numerals and signs used in FIGS. 1 and 2.

Example 1

FIGS. 1 and 2 (FIG. 1 is a diagram illustrating a lens system configuration at the wide-angle end, FIG. 2 is a diagram illustrating arrangement of the respective lens groups at the wide-angle end (W) and the telephoto end (T)) show the following configuration. The wide-angle projection zoom lens according to Example 1 includes, in order from the magnification side: a first lens group G₁ that remains stationary during zooming, has a negative refractive power, and is used for focusing; a second lens group G₂ that is movable during zooming and has a positive refractive power; a third lens group G₃ that is movable during zooming and has a negative refractive power; a fourth lens group G₄ that is movable during zooming and has a positive refractive power; a fifth lens group G₅ that remains stationary during zooming, has a positive refractive power, and is used to fix a position of a pupil. The projection zoom lens is configured to be telecentric on the reduction side. Further, an image display surface 1 of the light valve and a glass block 2 are arranged on the reduction side of the fifth lens group G₅ in this order from the reduction side. Furthermore, the three movable zoom lens groups G₂ to G₄ are configured to be moved independently from each other during zooming.

Further, during zooming from the wide-angle end to the telephoto end, the first lens group G₁ and the fifth lens group G₅ remain stationary, and the second lens group G₂, the third lens group G₃, and the fourth lens group G₄ are independently movable in a direction of the optical axis Z so as to narrow a space between the first lens group G₁ and the second lens group G₂ and widen a space between the fourth lens group G₄ and the fifth lens group G₅.

As described above, the first lens group G₁ includes five lenses (first lens L₁ to fifth lens L₅) successively arranged to have negative, negative, negative, positive, negative refractive powers in order from the most magnification side. The first lens L₁ is formed as a plastic lens, of which both surfaces are aspheric, having a negative refractive power in the paraxial region, and the second lens L₂ is formed as a negative meniscus lens concave toward the reduction side, and the third lens L₃ is formed as a biconcave lens. Further, the fourth lens L₄ is formed as a biconvex lens, and the fifth lens L₅ is formed as a plastic lens, of which both surfaces are aspheric, having a small negative refractive power in the paraxial region.

Further, the second lens group G₂ includes a sixth lens L₆ formed as a biconvex lens and a seventh lens L₇ formed as a positive meniscus lens convex toward the magnification side.

Furthermore, the third lens group G₃ includes an eighth lens L₈ formed as a biconcave lens and a ninth lens L₉ formed as a biconvex lens.

Further, the fourth lens group G₄ includes a tenth lens L₁₀ formed as a negative meniscus lens convex toward the magnification side, an eleventh lens L₁₁ formed as a biconvex lens, a twelfth lens L₁₂ formed as a negative meniscus lens convex toward the reduction side, a thirteenth lens L₁₃ formed as a biconcave lens, a fourteenth lens L₁₄ formed as a biconvex lens, and a fifteenth lens L₁₅ formed as a biconvex lens. Furthermore, the eleventh lens L₁₁ and the twelfth lens L₁₂ (cemented surface is formed in a shape concave toward the magnification side) are cemented to each other. In addition, the thirteenth lens L₁₃ and the fourteenth lens L₁₄ (cemented surface is formed in a shape concave toward the reduction side) are cemented to each other.

Further, the fifth lens group G₅ for fixing the pupil position includes only a sixteenth lens L₁₆ formed as a biconvex lens.

Shapes of the aspheric surfaces in the first lens L₁ and the fifth lens L₅ are defined by the following aspheric expression. In these first lens L₁ and fifth lens L₅, it is possible to obtain an aberration correction effect even when any one surface of the lens is formed as an aspheric surface. However, it is more preferable that both surfaces of the lens be formed as aspheric surfaces.

$\begin{matrix} {Z = {\frac{Y^{2}/R}{1 + \sqrt{1 - {K \times {Y^{2}/R^{2}}}}} + {\sum\limits_{i = 2}^{6}{A_{2i}Y^{2i}}}}} & \left\lbrack {{Numerical}\mspace{14mu}{Expression}\mspace{14mu} 1} \right\rbrack \end{matrix}$

where

Z is a length of a perpendicular from a point on an aspheric surface, which is apart from the optic axis at a distance Y, to a tangential plane (a plane perpendicular to the optic axis) of the top of the aspheric surface,

Y is a distance from the optic axis,

R is a radius of curvature of an aspheric surface near the optic axis,

K is an eccentricity, and

A_(2i) is an aspheric surface coefficient (i=2 to 6).

The upper part of Table 1 shows radius of curvatures R (mm) of the lens surfaces of the projection lens system according to Example 1, center thicknesses of the lenses and air spaces between the lenses D (mm) (hereinafter, those are referred to as “on-axis surface spacings”), refractive indices N_(d) of the lenses at the d-line, and Abbe numbers ν_(d) of the lenses at the d-line. Furthermore, in Table 1 and the following tables, each numeral of the surface numbers represents the order from the magnification side, and each surface having the reference sign * attached to the right side of each surface number is an aspheric surface. In Example 1 and the following Example 2, the radius of curvatures R of the aspheric surfaces of those are represented as values of the radius of curvatures on the optical axis Z in the respective tables. However, in the corresponding lens configuration diagrams, some of the extracted lines may not be extracted from the intersection between the lens surfaces and the optical axis Z for convenience of description.

Further, as described above, in the wide-angle projection zoom lens according to Example 1, the movable zoom lens groups G₂ to G₄ are configured to be moved independently from each other in the direction of the optical axis Z during zooming. The lower part of Table 1 shows values of the variable spaces (D₁₀, D₁₄, D₁₈, and D₂₈) at the wide-angle end (WIDE) and telephoto end (TELE) and the medium position (MEDIUM) therebetween.

Further, Table 2 shows values of the respective constants K, A₄, A₆, A₈, A₁₀, and A₁₂ corresponding to the respective aspheric surfaces.

TABLE 1 FOCAL LENGTH: 9.77-12.69, ANGLE OF VIEW: 96.7 DEGREES, SPEED: F1.70-1.88 Surface Effective Number R D Diameter N_(d) ν_(d)  1* 249.4857 5.800 80.73 1.49100 57.6  2* 54.3104 16.311  73.36  3 272.8409 1.640 51.80 1.79952 42.2  4 22.7995 13.698  37.68  5 −52.6320 1.670 37.54 1.48749 70.2  6 47.3655 4.683 36.95  7 163.6437 5.305 37.61 1.83400 37.2  8 −78.1391 2.233 37.75  9* 56.0901 3.400 35.95 1.49100 57.6 10* 35.0287 **(Variable 1) 34.95 11 49.1828 4.921 32.66 1.71472 52.6 12 −124.4484 0.419 32.28 13 46.3317 2.599 29.06 1.74407 27.8 14 111.3993 **(Variable 2) 28.41 15 −127.5123 1.400 20.71 1.71334 53.9 16 20.0425 0.500 18.83 17 20.4155 6.103 18.85 1.48730 70.5 18 −85.8969 **(Variable 3) 18.00 19 31.1272 1.140 16.71 1.80518 25.4 20 21.9262 1.322 16.33 21 74.8072 5.377 16.38 1.48749 70.2 22 −14.6213 1.540 17.02 1.83400 37.2 23 −76.5371 1.638 19.03 24 −46.6118 1.540 19.98 1.83400 37.2 25 81.6510 4.856 22.40 1.49700 81.6 26 −28.7184 0.200 23.88 27 115.3236 6.695 27.67 1.49700 81.6 28 −25.5457 **(Variable 4) 28.51 29 54.8801 4.444 31.41 1.80498 45.6 30 −251.7329 12.740  31.13 31 ∞ 25.500  27.11 1.51633 64.1 32 ∞ 0.200 22.06 D₁₀ D₁₄ D₁₈ D₂₈ (Variable 1) (Variable 2) (Variable 3) (Variable 4) WIDE 21.875 8.987 9.326 0.500 MEDIUM 16.217 12.105 5.917 6.452 TELE 11.824 15.909 1.000 11.960 *Aspheric Surface **Variable Space

TABLE 2 * Aspheric Coefficient Surface Number K A₄ A₆ 1st Surface 1.000000   7.7658398E−06 −5.3631839E−09 2nd Surface 1.000000   3.9805157E−06 −3.6043609E−09 9th Surface 1.000000 −2.5760940E−05   3.2744074E−08 10th Surface 1.000000 −2.8407899E−05   3.1951856E−08 Surface Number A₈ A₁₀ A₁₂ 1st Surface   3.4952277E−12 −1.2921198E−15   2.5463431E−19 2nd Surface −2.3889191E−12   2.6035371E−15 −6.4328160E−19 9th Surface −3.5095364E−11   3.9581937E−14 −1.9128572E−17 10th Surface −1.8871314E−11 −2.7396853E−14   6.4028294E−17

Example 2

As shown in FIGS. 3 and 4 (FIG. 3 is a diagram illustrating a lens system configuration at the wide-angle end, FIG. 4 is a diagram illustrating arrangement of the respective lens groups at the wide-angle end (W) and the telephoto end (T)), the wide-angle projection zoom lens according to Example 2 has substantially the same configuration as the wide-angle projection zoom lens according to Example 1. However, in the wide-angle projection zoom lens according to Example 2, there is a difference in that the fourth lens group G₄ includes a tenth lens L₁₀ formed as a negative meniscus lens convex toward the magnification side, an eleventh lens L₁₁ formed as a biconvex lens, a twelfth lens L₁₂ formed as a biconcave lens, a thirteenth lens L₁₃ formed as a biconvex lens, and a fourteenth lens L₁₄ formed as a biconvex lens. In addition, there is another difference in that the eleventh lens L₁₁, the twelfth lens L₁₂, and the thirteenth lens L₁₃ constitute a three-element cemented lens (the cemented surface between the eleventh lens L₁₁ and the twelfth lens L₁₂ has a shape concave toward the magnification side, and the cemented surface between the twelfth lens L₁₂ and the thirteenth lens L₁₃ has a shape concave toward the reduction side).

Further, the fifth lens group G₅ includes only the fifteenth lens L₁₅ formed as a biconvex lens.

The upper part of Table 3 shows radius of curvatures R (mm) of the lens surfaces of the projection lens system according to Example 2, center thicknesses of the lenses and air spaces between the lenses D (mm), refractive indices N_(d) of the lenses at the d-line, and Abbe numbers ν_(d) of the lenses at the d-line.

Further, as described above, in the wide-angle projection zoom lens according to Example 2, the movable zoom lens groups G₂ to G₄ are configured to be moved independently from each other in the direction of the optical axis Z during zooming. The lower part of Table 3 shows values of the variable spaces (D₁₀, D₁₄, D₁₈, and D₂₆) at the wide-angle end (WIDE) and telephoto end (TELE) and the medium position (MEDIUM) therebetween.

Further, Table 4 shows values of the respective constants K, A₄, A₆, A₈, A₁₀, and A₁₂ corresponding to the respective aspheric surfaces.

TABLE 3 FOCAL LENGTH: 9.77-12.70, ANGLE OF VIEW: 96.8 DEGREES, SPEED: F1.70-1.83 Surface Effective Number R D Diameter N_(d) ν_(d)  1* 230.9465 5.800 80.94 1.49100 57.6  2* 54.0935 17.259  73.66  3 238.4338 1.640 49.73 1.79952 42.2  4 21.7971 13.071  36.16  5 −53.0745 1.672 36.01 1.48749 70.2  6 48.1734 4.756 35.44  7 202.1564 4.723 36.08 1.83400 37.2  8 −77.3787 1.997 36.21  9* 49.0895 3.400 34.94 1.49100 57.6 10* 33.8425 **(Variable 1) 33.85 11 50.7372 4.558 31.30 1.71747 52.6 12 −117.0663 0.419 31.01 13 45.6639 2.416 29.01 1.71514 29.2 14 130.2590 **(Variable 2) 28.60 15 −131.4544 1.400 20.55 1.71409 53.9 16 19.9216 0.500 18.73 17 20.6205 5.803 18.78 1.48527 70.6 18 −89.2866 **(Variable 3) 18.00 19 33.6368 1.140 17.00 1.80518 25.4 20 22.0070 1.452 16.50 21 99.7417 8.158 16.65 1.48749 70.2 22 −14.6961 2.080 18.55 1.83400 37.2 23 66.1370 4.590 22.53 1.49700 81.6 24 −34.7339 0.200 23.89 25 121.3280 8.135 26.94 1.49700 81.6 26 −24.1755 **(Variable 4) 28.51 27 56.2265 4.388 31.25 1.80497 45.6 28 −200.5265 12.740  31.01 29 ∞ 25.500  27.02 1.51633 64.1 30 ∞ 0.156 22.04 D₁₀ D₁₄ D₁₈ D₂₆ (Variable 1) (Variable 2) (Variable 3) (Variable 4) WIDE 21.906 8.857 9.373 0.500 MEDIUM 16.452 12.047 5.905 6.236 TELE 12.181 15.868 1.000 11.594 *Aspheric Surface **Variable Space

TABLE 4 * Aspheric Coefficient Surface Number K A₄ A₆ 1st Surface 1.0000000   7.7372868E−06 −5.2841080E−09 2nd Surface 1.0000000   4.1677379E−06 −3.7306393E−09 9th Surface 1.0000000 −2.5830702E−05   3.4050162E−08 10th Surface 1.0000000 −2.8375183E−05   3.4221005E−08 Surface Number A₈ A₁₀ A₁₂ 1st Surface   3.4205977E−12 −1.2503911E−15 2.4423810E−19 2nd Surface −2.0495206E−12   2.2969719E−15 −5.5992772E−19   9th Surface −2.9149668E−11   1.4327304E−14 1.9470022E−17 10th Surface −2.0535300E−11 −4.2708917E−14 1.0059607E−16

Example 3

As shown in FIGS. 5 and 6 (FIG. 5 is a diagram illustrating a lens system configuration at the wide-angle end, FIG. 6 is a diagram illustrating arrangement of the respective lens groups at the wide-angle end (W) and the telephoto end (T)), the wide-angle projection zoom lens according to Example 3 has substantially the same configuration as the wide-angle projection zoom lens according to Example 1.

The upper part of Table 5 shows radius of curvatures R (mm) of the lens surfaces of the projection lens system according to Example 3, center thicknesses of the lenses and air spaces between the lenses D (mm), refractive indices N_(d) of the lenses at the d-line, and Abbe numbers ν_(d) of the lenses at the d-line.

Further, as described above, in the wide-angle projection zoom lens according to Example 3, the movable zoom lens groups G₂ to G₄ are configured to be moved independently from each other in the direction of the optical axis Z during zooming. The lower part of Table 5 shows values of the variable spaces (D₁₀, D₁₄, D₁₈, and D₂₈) at the wide-angle end (WIDE) and telephoto end (TELE) and the medium position (MEDIUM) therebetween.

Further, Table 6 shows values of the respective constants K, A₄, A₆, A₈, A₁₀, and A₁₂ corresponding to the respective aspheric surfaces.

TABLE 5 FOCAL LENGTH: 9.77-12.64, ANGLE OF VIEW: 96.7 DEGREES, SPEED: F1.70-1.87 Surface Effective Number R D Diameter N_(d) ν_(d)  1* 250.9682 5.800 80.54 1.49100 57.6  2* 54.3304 16.285  73.20  3 289.4217 1.640 51.64 1.79952 42.2  4 22.8386 13.894  37.63  5 −52.5884 1.668 37.34 1.48749 70.2  6 49.4984 4.352 36.79  7 143.5493 5.197 37.42 1.83400 37.2  8 −79.0142 2.514 37.50  9* 58.7539 3.400 35.56 1.49100 57.6 10* 35.4363 **(Variable 1) 34.51 11 50.8707 4.666 31.42 1.71467 52.6 12 −124.4893 0.417 31.01 13 44.7495 2.649 28.01 1.74328 27.8 14 118.6956 **(Variable 2) 27.42 15 −125.2225 1.400 20.34 1.71296 53.9 16 19.9689 0.500 18.80 17 20.4030 6.046 18.85 1.48744 70.3 18 −79.6796 **(Variable 3) 18.00 19 32.7472 1.140 16.51 1.84666 23.8 20 21.9464 1.330 16.00 21 75.5232 5.445 16.18 1.48749 70.2 22 −14.7996 1.540 17.05 1.83400 37.2 23 −74.9823 1.517 19.08 24 −45.5751 1.540 19.93 1.83400 37.2 25 84.5007 4.878 22.22 1.49700 81.6 26 −28.7980 0.200 23.78 27 113.7360 6.862 27.55 1.49700 81.6 28 −25.7468 **(Variable 4) 28.51 29 55.7885 4.366 31.26 1.80498 45.6 30 −217.5201 12.740  31.01 31 ∞ 25.500  27.03 1.51633 64.1 32 ∞ 0.193 22.05 D₁₀ D₁₄ D₁₈ D₂₈ (Variable 1) (Variable 2) (Variable 3) (Variable 4) WIDE 23.335 8.503 8.528 0.500 MEDIUM 17.496 11.427 5.442 6.500 TELE 13.051 14.926 1.000 11.897 *Aspheric Surface **Variable Space

TABLE 6 * Aspheric Coefficient Surface Number K A₄ A₆ 1st Surface 1.000000   7.8029935E−06 −5.2819701E−09 2nd Surface 1.000000   4.0133673E−06 −3.3369476E−09 9th Surface 1.000000 −2.5999802E−05   3.2151930E−08 10th Surface 1.000000 −2.8364225E−05   2.9684241E−08 Surface Number A₈ A₁₀ A₁₂ 1st Surface   3.3618896E−12 −1.2136942E−15   2.3568854E−19 2nd Surface −2.9878183E−12   2.9973137E−15 −7.2897925E−19 9th Surface −4.1716969E−11   6.9999815R−14 −5.6763886E−17 10th Surface −1.6737442E−11 −1.6387514E−14   4.1852690E−17

Example 4

As shown in FIGS. 7 and 8 (FIG. 7 is a diagram illustrating a lens system configuration at the wide-angle end, FIG. 8 is a diagram illustrating arrangement of the respective lens groups at the wide-angle end (W) and the telephoto end (T)), the wide-angle projection zoom lens according to Example 4 has substantially the same configuration as the wide-angle projection zoom lens according to Example 2. However, there is a difference in that the fifth lens group G₅ includes the fifteenth lens L₁₅ formed as a positive meniscus lens convex toward the magnification side.

The upper part of Table 7 shows radius of curvatures R (mm) of the lens surfaces of the projection lens system according to Example 4, center thicknesses of the lenses and air spaces between the lenses D (mm), refractive indices N_(d) of the lenses at the d-line, and Abbe numbers ν_(d) of the lenses at the d-line.

Further, as described above, in the wide-angle projection zoom lens according to Example 4, the movable zoom lens groups G₂ to G₄ are configured to be moved independently from each other in the direction of the optical axis Z during zooming. The lower part of Table 7 shows values of the variable spaces (D₁₀, D₁₄, D₁₈, and D₂₆) at the wide-angle end (WIDE) and telephoto end (TELE) and the medium position (MEDIUM) therebetween.

Further, Table 8 shows values of the respective constants K, A₄, A₆, A₈, A₁₀, and A₁₂ corresponding to the respective aspheric surfaces.

TABLE 7 FOCAL LENGTH: 9.77-12.55, ANGLE OF VIEW: 96.8 DEGREES, SPEED: F1.70-1.79 Surface Effective Number R D Diameter N_(d) ν_(d)  1* 227.6009 5.800 77.12 1.49100 57.6  2* 53.2898 17.672  70.51  3 277.9984 1.640 47.77 1.78590 44.2  4 20.3011 12.080  34.14  5 −57.1830 1.617 34.07 1.48749 70.2  6 49.5603 1.983 33.40  7 104.4830 3.898 33.50 1.83400 37.2  8 −106.9864 2.460 33.47  9* 50.7263 3.400 32.35 1.49100 57.6 10* 36.7131 **(Variable 1) 31.24 11 48.2046 4.823 26.92 1.83481 42.7 12 −147.5374 0.451 26.06 13 51.2213 2.920 24.00 1.74077 27.8 14 127.4922 **(Variable 2) 23.28 15 −97.8312 1.400 18.20 1.71300 53.9 16 23.8908 0.112 17.41 17 25.2796 3.452 17.41 1.48749 70.2 18 −130.1543 **(Variable 3) 17.20 19 41.6582 1.140 16.88 1.84666 23.8 20 23.7308 0.723 16.50 21 50.0057 10.286  16.48 1.48749 70.2 22 −13.7027 1.640 18.76 1.83400 37.2 23 105.9616 5.960 22.74 1.49700 81.6 24 −28.6139 0.200 25.00 25 180.6368 6.836 29.29 1.49700 81.6 26 −24.2011 **(Variable 4) 29.96 27 52.3339 3.728 33.57 1.83481 42.7 28 −1317.8137 12.740  33.40 29 ∞ 25.500  28.46 1.51633 64.1 30 ∞ 0.190 22.07 D₁₀ D₁₄ D₁₈ D₂₆ (Variable 1) (Variable 2) (Variable 3) (Variable 4) WIDE 21.023 7.398 7.356 0.500 MEDIUM 15.752 10.257 4.412 5.843 TELE 12.483 12.964 1.000 9.840 *Aspheric Surface **Variable Space

TABLE 8 * Aspheric Coefficient Surface Number K A₄ A₆ 1st Surface 1.0000000   1.0971089E−05 −1.1388973E−08 2nd Surface 1.0000000   8.4521747E−06 −1.2723925E−08 9th Surface 1.0000000 −2.5423272E−05   3.5322947E−08 10th Surface 1.0000000 −2.6418329E−05   3.5829905E−08 Surface Number A₈ A₁₀ A₁₂ 1st Surface   1.0761899E−11 −5.7168138E−15 1.4813578E−18 2nd Surface   8.7750655E−12 −4.1195975E−15 8.5365947E−19 9th Surface −2.4040329E−11 −2.8386416E−13 8.4600663E−16 10th Surface −6.2485432E−11 −1.6291137E−13 7.9802341E−16

Further, FIGS. 9 to 12 are aberration diagrams illustrating various aberrations, spherical aberration, distortion, astigmatism, and lateral chromatic aberration at the wide-angle end (WIDE), the medium position (MEDIUM), and the telephoto end (TELE) of the wide-angle projection zoom lenses according to Examples 1 to 4. In each aberration diagram, ω represents a half angle of view. The aberration diagrams of spherical aberrations show aberration curves at the respective wavelengths of G (green), B (blue) and R (red). The aberration diagrams of lateral chromatic aberrations show aberration curves of B and R relative to G. As shown in FIGS. 9 to 12, in the wide-angle projection lens described in Examples 1 to 4, not only distortion and chromatic aberration but also the other aberrations are well corrected. Thus, the wide-angle projection lens is formed as a wide-angle and fast projection lens having a half angle of view in the range of 48.3 to 48.4 degrees and an F number of 1.70 at the wide-angle end.

Further, the wide-angle projection zoom lens according to the invention is not limited to the examples mentioned above, and may be modified to various forms. For example, it may be possible properly to modify the radius of curvatures R of the lenses and the on-axis spacing D.

Furthermore, the projection type display apparatus according to the invention is not limited to the configurations mentioned above, and may be modified to various forms of apparatuses having the wide-angle projection zoom lens according to the invention. As the light valve, it may be possible to use a transmissive or reflective liquid crystal display device, or a micro mirror device (for example, a digital micro mirror device manufactured by Texas Instruments Co.) in which a plurality of inclinable micro mirrors are formed on a substantially flat surface. As the illumination optical system, it may be possible to employ a proper configuration corresponding to types of the light valves. 

1. A wide-angle projection zoom lens, which is telecentric on a reduction side, comprising, in order from a magnification side: a first lens group having a negative refractive power; a second lens group having a positive refractive power; a third lens group having a negative refractive power; a fourth lens group having a positive refractive power; and a fifth lens group having a positive refractive power, wherein during zooming from a wide-angle end to a telephoto end, the first lens group and the fifth lens group remain stationary, and the second lens group, the third lens group, and the fourth lens group are movable in a direction of an optical axis so as to narrow a space between the first lens group and the second lens group and widen a space between the fourth lens group and the fifth lens group, and wherein the first lens group includes five lenses having negative, negative, negative, positive, negative refractive powers in order from the magnification side, and in the first lens group, the negative lens closest to the magnification side and the negative lens closest to the reduction side are formed as aspheric lenses made of plastic.
 2. The wide-angle projection zoom lens according to claim 1, wherein the second lens group includes two positive lenses.
 3. The wide-angle projection zoom lens according to claim 1, wherein the third lens group includes a negative lens and a positive lens in order from the magnification side, and in the third lens group, a surface of the negative lens on the reduction side is formed as a concave surface, and a surface of the positive lens on the magnification side is formed as a convex surface.
 4. The wide-angle projection zoom lens according to claim 1, wherein the fourth lens group includes, in order from the magnification side: a negative meniscus lens convex toward the magnification side; a first cemented lens having a cemented surface formed in a shape concave toward the magnification side; a second cemented lens having a cemented surface formed in a shape concave toward the reduction side; and a positive lens.
 5. The wide-angle projection zoom lens according to claim 1, wherein the fourth lens group includes, in order from the magnification side: a negative meniscus lens convex toward the magnification side; a three-element cemented lens having, in order from a magnification side, a first cemented surface formed in a shape concave toward the magnification side and a second cemented surface formed in a shape concave toward the reduction side; and a positive lens.
 6. The wide-angle projection zoom lens according to claim 1, wherein the fifth lens group includes a single positive lens.
 7. A projection type display apparatus comprising: a light source; a light valve; an illumination optical unit guiding rays originated from the light source into the light valve; and the wide-angle projection zoom lens, which is telecentric on the reduction side, according to claim 1, wherein the rays originated from the light source are optically modulated by the light valve, and are projected onto a screen by the wide-angle projection zoom lens.
 8. The wide-angle projection zoom lens according to claim 2, wherein the third lens group includes a negative lens and a positive lens in order from the magnification side, and in the third lens group, a surface of the negative lens on the reduction side is formed as a concave surface, and a surface of the positive lens on the magnification side is formed as a convex surface.
 9. The wide-angle projection zoom lens according to claim 8, wherein the fourth lens group includes, in order from the magnification side: a negative meniscus lens convex toward the magnification side; a first cemented lens having a cemented surface formed in a shape concave toward the magnification side; a second cemented lens having a cemented surface formed in a shape concave toward the reduction side; and a positive lens.
 10. The wide-angle projection zoom lens according to claim 9, wherein the fifth lens group includes a single positive lens.
 11. A projection type display apparatus comprising: a light source; a light valve; an illumination optical unit guiding rays originated from the light source into the light valve; and the wide-angle projection zoom lens, which is telecentric on the reduction side, according to claim 10, wherein the rays originated from the light source are optically modulated by the light valve, and are projected onto a screen by the wide-angle projection zoom lens.
 12. The wide-angle projection zoom lens according to claim 8, wherein the fourth lens group includes, in order from the magnification side: a negative meniscus lens convex toward the magnification side; a three-element cemented lens having, in order from a magnification side, a first cemented surface formed in a shape concave toward the magnification side and a second cemented surface formed in a shape concave toward the reduction side; and a positive lens.
 13. The wide-angle projection zoom lens according to claim 12, wherein the fifth lens group includes a single positive lens.
 14. A projection type display apparatus comprising: a light source; a light valve; an illumination optical unit guiding rays originated from the light source into the light valve; and the wide-angle projection zoom lens, which is telecentric on the reduction side, according to claim 13, wherein the rays originated from the light source are optically modulated by the light valve, and are projected onto a screen by the wide-angle projection zoom lens. 